As used herein, the terms “user agent” and “UA” can refer to mobile devices such as mobile telephones, personal digital assistants, handheld or laptop computers, and similar devices that have telecommunications capabilities. Such a UA might consist of a wireless device and its associated Universal Integrated Circuit Card (UICC) that includes a Subscriber Identity Module (SIM) application, a Universal Subscriber Identity Module (USIM) application, or a Removable User Identity Module (R-UIM) application or might consist of the device itself without such a card. The term “UA” may also refer to devices that have similar capabilities but that are not transportable, such as desktop computers, set-top boxes, or network nodes. A UA might communicate with a second UA, some other element in a telecommunications network, an automated computing device such as a server computer, or some other device. A communications connection between a UA and another component might promote a voice call, a file transfer, or some other type of data exchange, any of which can be referred to as a call or a session.
In traditional wireless telecommunications systems, transmission equipment in a base station transmits signals throughout a geographical region known as a cell. As technology has evolved, more advanced equipment has been introduced that can provide services that were not possible previously. This advanced equipment might include, for example, an evolved node B (ENB) rather than a base station or other systems and devices that are more highly evolved than the equivalent equipment in a traditional wireless telecommunications system. Such advanced or next generation equipment may be referred to herein as long-term evolution (LTE) equipment, and a packet-based network that uses such equipment can be referred to as an evolved packet system (EPS). As used herein, the term “access device” will refer to any component, such as a traditional base station or an LTE ENB that can provide a UA with access to other components in a telecommunications system. In the EPS system, a user agent is referred to as user equipment.
Some UAs have the capability to communicate in a packet switched mode, wherein a data stream representing a portion of a call or session is divided into packets that are given unique identifiers. The packets might then be transmitted from a source to a destination along different paths and might arrive at the destination at different times. Upon reaching the destination, the packets are reassembled into their original sequence based on the identifiers. Voice over Internet Protocol (VoIP) is a well-known system for packet switched-based voice communication over the Internet. The term “VoIP” will refer herein to any packet switched voice call connected via the Internet, regardless of the specific technology that might be used to make the call.
For a wireless VoIP call, the signal that carries data between a UA and an access device can have a specific set of frequency, code, and time parameters and other characteristics that might be specified by the access device. A connection between a UA and an access device that has a specific set of such characteristics can be referred to as a resource. An access device typically establishes a different resource for each UA with which it is communicating at any particular time.